The tooth surface is normally covered by a layer of adsorbed salivary proteins which form an integument termed the acquired enamel pellicle. This structure contains the sites to which cariogenic organisms become attached. It therefore plays an important role in the initial stages of plaque formation and becomes interposed between the plaque and the underlying enamel. Since it acts as a diffusion barrier, it could readily control both the intensity of carious attack of the tooth and the rate of loss of the products of its demineralization. Thus the pellicle has the potential to exert a significant effect upon processes which lead to the development of carious lesions. The purpose of the proposed research is to study the nature of the acquired pellicle and to determine its properties. To this end, it is proposed that the pellicle precursors be identified and their compositions and properties be determined. The nature of the active groups, present in the precursors, which enable them to attach to the enamel surface and to each other, will be studied. The features of the pellicle which enable it to control ionic transport between the plaque and the enamel will be examined. The precursor proteins and the pellicle will be studied to determine the nature and properties of the active sites which are important in mediating bacterial attachment. The data obtained from this research will lead to an improved understanding of specific and important stages in the carious process, and may permit a more rational approach to be made to the development of methods for the prevention of both dental caries and periodontal disease than is presently possible.